Rubber compositions are sometimes prepared which contain a combination of particulate reinforcing filler comprised of amorphous, synthetic silica such as precipitated silica and fumed silica (sometimes referred to as precipitated and/or fumed silica) and rubber reinforcing carbon black.
A silica coupler is typically included to react with the precipitated and/or fumed silica surface and to interact with diene-based elastomers to thereby couple the silica to the rubber and aid in its reinforcement of the rubber.
Historically, rubber compositions have been prepared by blending separate and different rubber masterbatches which collectively contain combinations of silica and carbon black reinforcing fillers together with a silica coupler for the silica. Such separate rubber composition masterbatches may be, for example, a silica-rich rubber composition and a carbon black-rich rubber composition, for which at least one of the silica reinforcement containing rubber compositions also contains a silica coupler, and where the individual rubber masterbatches are subsequently mixed together. For example, see U.S. Pat. Nos. 5,696,197 and 5,773,504.
However, adding the silica coupler to the silica reinforcement-containing rubber creates a reactive mixture, namely a mixture where a moiety of the silica coupler is reactive with, and therefore reacts with, hydroxyl groups contained on the silica filler and another and different moiety of the silica coupler is interactive with diene-based elastomers.
In such circumstance, the rubber mixture must be mixed more carefully than conventional rubber mixtures such as, for example, by more carefully paying attention to and controlling a combination of mixing temperature profile parameters combined with appropriate mixing periods.
For this invention it is proposed to provide two rubber compositions, namely a silica-rich rubber compound and a carbon black-rich rubber compound without silica coupler and without sulfur curatives.
The silica-rich rubber compound would contain most, and perhaps all, of the silica reinforcement for the final rubber composition. The carbon black-rich rubber compound would contain most, and perhaps all, of the rubber reinforcing carbon black for the final rubber composition. None of these rubber compounds would contain the silica coupler so, in that sense, the two individual rubber compounds would not be silica coupler-containing reactive rubber compounds. Each of the rubber compounds could be prepared by mixing the respective rubber compounds in an internal rubber mixer or on an open cylindrical mill after which the two rubber compounds could be individually stored and would be mixed together in desirable ratios.
In the description of this invention, the terms “rubber” and “elastomer” where herein, are used interchangeably, unless otherwise provided. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art. The terms “cure” and “vulcanize” may be used interchangeably unless otherwise provided. In the description of this invention, the term “phr” refers to parts of a respective material per 100 parts by weight of rubber, or elastomer.